Adrenergic Agonists — MCQs
Which sympathomimetic drug is primarily known to increase heart rate?
The α2 agonist used in glaucoma is:
Effects of beta blockers on the heart are all of the following except:
Which of the following is a long-acting beta-2 agonist?
A chronic smoker was on nicotine replacement therapy and clonidine tablets for smoking de-addiction. He stopped taking clonidine tablets and now presents with a headache. What is the reason behind this condition?
Which of the following is a selective beta-1 agonist?
Match the following: Column A: a. Beta 1 b. Beta 2 c. Beta 3 Column B: 1. Mirabegron 2. Betaxolol 3. Salbutamol
Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)
Which of the following statements about clonidine is incorrect?
Which of the following drugs decreases plasma renin activity
Adrenergic Agonists Indian Medical PG Practice Questions and MCQs
Question 1: Which sympathomimetic drug is primarily known to increase heart rate?
- A. Isoprenaline (Correct Answer)
- B. Phenylephrine
- C. Noradrenaline
- D. Adrenaline
Explanation: ***Isoprenaline*** - **Isoprenaline** (isoproterenol) is a non-selective beta-adrenergic agonist, with a strong affinity for **β1 and β2 receptors** [1]. - Its activation of **β1 receptors** in the heart leads to a significant increase in **heart rate (positive chronotropy)** and contractility (positive inotropy) [1]. - It is the **most potent chronotropic agent** among sympathomimetics and is primarily known for increasing heart rate [2]. *Phenylephrine* - **Phenylephrine** is a selective **α1 adrenergic agonist** that causes vasoconstriction [4]. - It increases blood pressure but typically causes **reflex bradycardia** (decreased heart rate) due to baroreceptor activation. - Does NOT directly increase heart rate. *Noradrenaline* - **Noradrenaline** (norepinephrine) primarily acts on **α1 receptors** causing vasoconstriction, and to a lesser extent on **β1 receptors** [3]. - While it can stimulate β1 receptors, its predominant effect is to increase **mean arterial pressure** through vasoconstriction, often causing **reflex bradycardia** [3]. *Adrenaline* - **Adrenaline** (epinephrine) acts on **α1, β1, and β2 receptors** [4]. While it does increase heart rate via **β1 receptor** stimulation, it also causes significant **vasoconstriction** (via α1) and **vasodilation** (via β2). - Its cardiovascular effects are more complex and dose-dependent compared to isoprenaline's specific chronotropic action.
Question 2: The α2 agonist used in glaucoma is:
- A. Brimonidine (Correct Answer)
- B. Guanabenz
- C. Guanfacine
- D. Tizanidine
Explanation: ***Correct: Brimonidine*** - **Brimonidine** is an **α2-adrenergic agonist** commonly used in the treatment of glaucoma - It works by reducing **aqueous humor production** and increasing **uveoscleral outflow**, thereby lowering intraocular pressure - Available as eye drops (0.1%, 0.15%, 0.2% concentrations) *Incorrect: Guanfacine* - **Guanfacine** is an **α2A-adrenergic agonist** primarily used to treat **attention deficit hyperactivity disorder (ADHD)** and **hypertension** - It does not have a primary role in glaucoma treatment *Incorrect: Guanabenz* - **Guanabenz** is an **α2-adrenergic agonist** that acts centrally to reduce **sympathetic outflow**, used mainly as an **antihypertensive agent** - It is not indicated for the treatment of glaucoma *Incorrect: Tizanidine* - **Tizanidine** is an **α2-adrenergic agonist** primarily used as a **muscle relaxant** to manage spasticity - It is not used for glaucoma
Question 3: Effects of beta blockers on the heart are all of the following except:
- A. Decreases duration of systole (Correct Answer)
- B. Decrease in heart rate
- C. May decrease cardiac output initially.
- D. May precipitate heart failure in acute settings.
Explanation: ***Decreases duration of systole*** - Beta-blockers primarily prolong the **duration of systole** by extending the **ejection time** and slowing ventricular relaxation. - They also increase the **diastolic filling time** by reducing heart rate, impacting overall cardiac cycle duration. *Decrease in heart rate* - Beta-blockers block **beta-1 adrenergic receptors** in the heart, leading to a decrease in **sympathetic stimulation** and thus a reduced heart rate. - This effect is beneficial in conditions like **tachycardia** and **angina**, as it reduces myocardial oxygen demand. *May decrease cardiac output initially.* - By reducing heart rate and contractility, beta-blockers can initially decrease **cardiac output**, especially in patients with pre-existing **ventricular dysfunction**. - This effect is often transient, as chronic use can lead to beneficial remodeling and improved efficiency in some conditions. *May precipitate heart failure in acute settings.* - In patients with acutely decompensated heart failure or severe left ventricular dysfunction, beta-blockers can acutely worsen cardiac function due to their **negative inotropic effects**. - Therefore, beta-blockers are typically initiated cautiously at low doses in stable heart failure patients and are contraindicated in acute decompensation.
Question 4: Which of the following is a long-acting beta-2 agonist?
- A. Isoprenaline
- B. Ephedrine
- C. Salbutamol
- D. Formoterol (Correct Answer)
Explanation: ***Formoterol*** - **Formoterol** is a **long-acting beta-2 agonist (LABA)** commonly used in the treatment of asthma and COPD. - It provides **bronchodilation** for up to 12 hours due to its high lipophilicity, allowing it to remain in the cell membrane and continuously activate beta-2 receptors. *Isoprenaline (non-selective adrenergic agonist)* - **Isoprenaline** is a **non-selective beta-adrenergic agonist**, meaning it activates both beta-1 and beta-2 receptors. - It is **short-acting** and primarily used as a vasodilator or to stimulate heart rate, not as a long-acting bronchodilator. *Ephedrine (non-selective adrenergic agonist)* - **Ephedrine** is a **mixed-acting sympathomimetic amine** that increases the release of norepinephrine and directly stimulates alpha and beta receptors. - It has a short duration of action and is primarily used as a decongestant or bronchodilator in emergency situations, not as a long-acting agent. *Salbutamol (short-acting beta-2 agonist)* - **Salbutamol** is a **short-acting beta-2 agonist (SABA)**, providing rapid onset but a short duration of action (typically 4-6 hours). - It is used for **relieving acute bronchospasm** and is not considered a long-acting medication for maintenance therapy.
Question 5: A chronic smoker was on nicotine replacement therapy and clonidine tablets for smoking de-addiction. He stopped taking clonidine tablets and now presents with a headache. What is the reason behind this condition?
- A. Postural hypotension
- B. Receptor upregulation
- C. Rebound hypertension (Correct Answer)
- D. Receptor hypersensitivity
Explanation: ***Rebound hypertension*** - **Clonidine withdrawal** can cause a sudden surge in blood pressure due to increased sympathetic activity, leading to **rebound hypertension** and symptoms like headaches. - This occurs because chronic clonidine use suppresses sympathetic outflow, and its abrupt discontinuation unmasks this suppressed activity, causing a hypertensive crisis. *Postural hypotension* - **Postural hypotension** is a common side effect of clonidine due to its vasodilatory effects, causing blood pressure to drop when standing. - However, the patient's headache following clonidine cessation is more indicative of a **hypertensive event**, not hypotension. *Receptor upregulation* - **Receptor upregulation** refers to an increase in the number of receptors, often in response to prolonged antagonism or decreased ligand exposure. - While receptor changes occur, the primary mechanism of clonidine withdrawal is the **overcompensation** of the sympathetic nervous system, not simply an increased number of receptors. *Receptor hypersensitivity* - **Receptor hypersensitivity** implies an exaggerated response to a normal concentration of a neurotransmitter, which can contribute to withdrawal symptoms. - While it plays a role, the more immediate and critical cause of the headache is the rapid increase in blood pressure due to **rebound sympathetic activity**.
Question 6: Which of the following is a selective beta-1 agonist?
- A. Terbutaline
- B. Albuterol
- C. Dobutamine (Correct Answer)
- D. Isoetharine
Explanation: ***Dobutamine*** - **Dobutamine** is a **selective beta-1 agonist** primarily used to increase **cardiac contractility** and output, making it valuable in cases of **heart failure** or **cardiogenic shock**. - Its selectivity for beta-1 receptors minimizes effects on **beta-2 receptors** in the lungs, reducing the risk of **bronchodilation** or **bronchospasm** compared to non-selective beta agonists. *Terbutaline* - **Terbutaline** is a **beta-2 selective agonist** primarily used as a **bronchodilator** in the treatment of **asthma** and **COPD**, and as a **tocolytic** to delay premature labor. - While it has some beta-1 activity at higher doses, its main therapeutic effect comes from **bronchodilation** via **beta-2 receptors**. *Albuterol* - **Albuterol** is a **short-acting beta-2 selective agonist (SABA)** used for the rapid relief of **bronchospasm** in conditions like **asthma**. - Its primary action is on **beta-2 receptors** in the airways, causing **bronchodilation**, and it has minimal activity on **beta-1 receptors** at therapeutic doses. *Isoetharine* - **Isoetharine** is a **beta-2 selective agonist** historically used as a **bronchodilator**, though it is less selective than newer agents like albuterol. - While predominantly acting on **beta-2 receptors**, it can have some **cardiac effects** (beta-1 stimulation) at higher doses, and has been largely replaced by more selective agents with better safety profiles.
Question 7: Match the following: Column A: a. Beta 1 b. Beta 2 c. Beta 3 Column B: 1. Mirabegron 2. Betaxolol 3. Salbutamol
- A. a-2, b-3 ,c-1 (Correct Answer)
- B. a-2, b-1, c-3
- C. a-3, b-2, c-1
- D. a-3, b-1, c-2
Explanation: ***a-2, b-3, c-1*** - This pairing correctly matches **Betaxolol** with **Beta 1 selective** antagonism, **Salbutamol** with **Beta 2 selective** agonism, and **Mirabegron** with **Beta 3 selective** agonism. - **Betaxolol** is a beta-1 selective adrenergic receptor antagonist, primarily used in ophthalmology to reduce intraocular pressure and as an antihypertensive. **Salbutamol** is a selective beta-2 adrenergic agonist used as a bronchodilator in asthma and COPD, causing relaxation of bronchial smooth muscle. **Mirabegron** is a selective beta-3 adrenergic agonist used to treat overactive bladder by relaxing the detrusor muscle. *a-2, b-1, c-3* - This option incorrectly assigns **Mirabegron** to Beta 2. Mirabegron is a **Beta 3 selective agonist**. - It also incorrectly assigns **Salbutamol** to Beta 3. Salbutamol is a **Beta 2 selective agonist**. *a-3, b-2, c-1* - This option incorrectly assigns **Salbutamol** to Beta 1. Salbutamol is a **Beta 2 selective agonist**. - It also incorrectly assigns **Betaxolol** to Beta 2. Betaxolol is a **Beta 1 selective antagonist**. *a-3, b-1, c-2* - This option incorrectly assigns **Salbutamol** to Beta 1 and **Betaxolol** to Beta 3. - **Salbutamol** is a Beta 2 selective agonist, and **Betaxolol** is a Beta 1 selective antagonist.
Question 8: Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)
- A. Drug in graph A is epinephrine
- B. Effect on heart in graph A can be overcome by antimuscarinic
- C. Drug acting on graph C is nor-epinephrine
- D. Drug acting on graph B is isoproterenol (Correct Answer)
Explanation: ***Drug acting on graph B is isoproterenol*** - Graph B shows a definite **increase in pulse rate** and a **decrease in peripheral resistance**, while blood pressure remains largely unchanged due to the combined effects. - **Isoproterenol** is a non-selective β-adrenergic agonist that causes increased heart rate (β1 effect) and vasodilation leading to decreased peripheral resistance (β2 effect). - This unique hemodynamic profile is characteristic of isoproterenol and distinguishes it from other catecholamines. *Drug in graph A is epinephrine* - Graph A shows a **decrease in pulse rate**, which is **not characteristic** of epinephrine at the dose shown (10 μg/min). - Epinephrine typically causes **tachycardia** due to β1-adrenergic stimulation, not bradycardia. - The cardiovascular profile in graph A does not match epinephrine's expected effects. *Effect on heart in graph A can be overcome by antimuscarinic* - The decreased pulse rate in graph A suggests **reflex bradycardia** or parasympathetic stimulation. - However, without knowing the actual drug, we cannot definitively state whether antimuscarinic agents would reverse this effect. - This option makes assumptions that cannot be verified from the graph alone. *Drug acting on graph C is nor-epinephrine* - Graph C shows **increased pulse rate** and **decreased peripheral resistance** with slight drop in blood pressure. - **Norepinephrine** primarily acts on α1-receptors, causing **vasoconstriction and increased peripheral resistance**, not decreased. - Norepinephrine would also increase blood pressure significantly, which contradicts the graph. - This cardiovascular profile does not match norepinephrine.
Question 9: Which of the following statements about clonidine is incorrect?
- A. Alpha 2 receptor agonist
- B. Sudden withdrawal causes rebound hypertension
- C. Controls loose motions due to diabetic neuropathy
- D. First line for AMI (Correct Answer)
Explanation: ***First line for AMI*** - Clonidine is **not first-line** for **Acute Myocardial Infarction (AMI)** as it can cause **bradycardia** and **hypotension**, potentially worsening cardiac output. - First-line AMI treatments include **thrombolytics**, **antiplatelet agents** (aspirin), **beta-blockers**, and **ACE inhibitors** for optimal cardiac protection. *Alpha 2 receptor agonist* - Clonidine is indeed an **alpha-2 adrenergic receptor agonist** that acts centrally in the **medulla oblongata**. - It reduces **sympathetic outflow** from the CNS, leading to decreased **heart rate**, **blood pressure**, and **peripheral vascular resistance**. *Sudden withdrawal causes rebound hypertension* - Abrupt clonidine discontinuation causes dangerous **rebound hypertension** due to sudden loss of **sympathetic inhibition**. - **Gradual tapering** over 1-2 weeks is essential to prevent this potentially life-threatening complication. *Controls loose motions due to diabetic neuropathy* - Clonidine effectively treats **diabetic diarrhea** by stimulating **alpha-2 receptors** in the enteric nervous system. - It **slows intestinal transit** and **enhances fluid absorption**, making it useful for **autonomic neuropathy-related** gastrointestinal symptoms.
Question 10: Which of the following drugs decreases plasma renin activity
- A. Nifedipine
- B. Hydralazine
- C. Enalapril
- D. Clonidine (Correct Answer)
Explanation: ***Clonidine*** - **Clonidine** is a centrally acting alpha-2 adrenergic agonist that reduces **sympathetic outflow** from the brainstem. - This reduction in sympathetic activity leads to decreased release of **norepinephrine**, which in turn reduces renin secretion by the kidneys. *Nifedipine* - **Nifedipine** is a **dihydropyridine calcium channel blocker** that causes peripheral vasodilation. - The vasodilation often leads to a **reflex increase in sympathetic activity** and, consequently, an increase in plasma renin activity. *Hydralazine* - **Hydralazine** is a direct systemic **vasodilator** that decreases peripheral vascular resistance. - This vasodilation can cause a **reflex increase in sympathetic activity** and **renin release** as the body tries to compensate for the drop in blood pressure. *Enalapril* - **Enalapril** is an **ACE inhibitor** that blocks the conversion of angiotensin I to angiotensin II. - This action directly leads to **increased plasma renin activity** due to the disruption of the negative feedback loop on renin release.
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